Long-term storage and/or disposal of radioactive waste is expensive. One way to reduce the cost and better utilize available storage and disposal space is to reduce the volume of the radioactive waste. Most radioactive waste includes large quantities of non-radioactive material, especially organic matter. This material may be removed and/or transformed into a more compact form to reduce the volume of the waste.
Thermal processing is one of the best ways to reduce the volume of waste. It may reduce the volume of wastes to levels that are not attainable using other methods. One common thermal processing method is incineration. It has been used for volume reduction in the municipal waste industry for decades.
Unfortunately, incineration has a number of drawbacks. One is that the reaction occurs at high temperatures in an oxygen-rich environment that facilitates the formation of dioxin and furan compounds, which are subject to heavy and increasing regulatory restrictions. Another is that the high temperature conditions volatilize radionuclides having relatively low boiling points such as cesium and technetium. These materials must be removed in downstream processes, which increases the complexity and cost of the process. The drawbacks have limited the application of incineration in the nuclear industry.
Steam reforming is one approach for the thermal volume reduction of organic matter in radioactive waste that has gained some traction in recent years. In a steam reforming process, the radioactive waste is fed into one or two fluidized bed reformers which are maintained at moderate temperatures and near ambient pressures to effect controlled oxidation and reduction reactions of the radioactive waste. The process allows for complete evaporation of water from the waste, destruction of organics, and conversion of nitrates into nitrogen gas without volatilizing radionuclides.
Although conventional steam reforming process have experienced some level of success and commercial acceptance, they still have a number of disadvantages. One disadvantage is that they require the addition of a solid combustible material to the reactor to provide energy for the pyrolysis and steam reforming reactions. The addition of this material increases the cost of the process and potentially reduces the degree of volume reduction due to the introduction of solid impurities in the material. Another disadvantage is that they generally cannot co-process different waste streams such as dry active waste (DAW), spent ion exchange resin (IER), and the like.
It would be desirable to have an integrated thermal process that may effectively process different waste streams to simplify and facilitate waste processing. It would be especially desirable for waste streams such as DAW and spent IER that differ substantially in their quantities and physical characteristics.